#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;
 
#include<bits/stdc++.h>
using namespace std;
 
vector<string> S={"C4", "D4", "E4", "F4", "G4", "A4", "B4"};
vector<double> B={261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5};

int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  
  int n;
  cin>>n;
  vector<double> A(n);
  rep(i,n) cin>>A[i];
  
  vector<double> score(7);
  rep(i,7){
    int d=n/B[i];
    double sum=0;
    for(int j=0;j+d<n;j++){
      sum+=abs(A[j]-A[j+d]);
    }
    score[i]=sum/(n-d);
  }
  double mi=1e18;
  int num=-1;
  rep(i,7){
    if(mi>score[i]){
      mi=score[i];
      num=i;
    }
  }
  cout<<S[num]<<endl;
    
  return 0;
}